a. Field of the Invention
The present invention generally relates to data communications in Small Computer System Interface (SCSI) systems, and more particularly, to high-speed data communications in Serial Attached SCSI (SAS) systems.
b. Background of Invention
Serial Attached SCSI (SAS) systems are used for providing serial connections between host computers and peripherals such as disk storage devices. In particular SAS devices may provide high speed serial data communications for the transfer of storage data under a SAS protocol data format. For example, second-generation SAS (SAS-2) devices may include data-rates of 6 Gb/s over a physical link, whereby each connection employs two-wires for providing differential signalling. Each physical link may operate in full-duplex mode by having 2 lanes for providing simultaneous differential signalling for both transmitting and receiving SAS data.
In order to maintain a low error-rate or error-free transmission environment in SAS systems, repeaters may be used to regenerate data. For example, SAS-2 6 Gb/s interfaces that drive greater than 20-30 inches of card (e.g., PCB Board) through multiple connectors to a SAS copper cable may typically require an active repeater module for connection between a SAS-2 Host Bus Adaptor and SAS-2 Bus Expander. However, the addition of one or more repeater modules introduces more complexity to the SAS system. For example, apart from an increased cost aspect, additional voltage regulation of the repeater module may be required. Also, the exchange of additional out-of-band control data is needed for configuring/re-configuring the operational requirements of the repeater module. Further, the repeater, as an active device, may be prone to failure, which would require a storage enclosure holding the repeater module to be powered down for replacement.
It may, therefore, be advantageous to, among other things, reduce or eliminate the use of repeater modules in SAS or other high-speed serial communication systems.